Who’s in Charge Inside Your Head?

[mike_c]

1. strictly speaking, they're parasitoids, not parasites....

Parasite-host relationships have a general tendency to evolve toward commensalism, while parasitoid-host relationships do not. The latter are more like predator-prey relationships, except each parasitoid kills a single host during it's life instead of multiple prey. Parasitoidism, as the OP describes it, is extremely successful and widespread among insects, especially among several fly and wasp families.